Embodiments of the present invention relate to an amplifier module, an amplification apparatus, to a transmitter having an amplifier stage, and a method for regulation of an amplification apparatus.
In any electronic communication system a transmitter includes an output amplifier, i.e. an amplification apparatus that boosts the power of a transmission signal to a level sufficient to allow for a reception of the transmission signal by a receiver. Particularly in a wireless communication system, such as defined by the GSM (Global System for Mobile Communication) standard or defined by UMTS (Universal Mobile Telecommunication Standard) or W-CDMA (Wideband Code Division Multiple Access), the power level of a mobile unit has to be adjusted according to rules given by a base station. A mobile terminal in a wireless communication system has to cope with changing environmental conditions. E.g. the operating temperature of the environment might be changing in a wide range. The 3GPP standard defines a range for the operating temperature between −10° C. up to 55° C. Real conditions can even be worse. Supply voltages in a mobile terminal may also vary, due to limited energy resources provided by a battery or accumulator cell. The supply voltage may be determined by the battery discharge characteristic and the voltage may thus drop during a transmit operation.
In addition the output amplifier may be subject to strict constraints on linearity and efficiency. If the transmitter is using an amplitude modulation such as 8-PSK modulation used in GSM EDGE (Enhanced Data GSM Environment), the output amplifier has to be arranged so that the output signal is linear in relation to the input signal to avoid a distortion of the output signal. Linearity and efficiency are also important in other modulation, such as GMSK (Gaussian Minimum Shift Keying).
The efficiency of the output amplifier is defined by the ratio of an outgoing power level at an output of the output amplifier to the power input into the output amplifier. The lower that ratio the more efficient the input power is brought onto the outgoing signal. This is advantageous if the transmitter is part of a mobile terminal having only limited power resources. It is known to perform power regulation in the mobile terminal. A known concept of controlling the power level is a so-called closed power loop, measuring the power level at an output of the output amplifier and comparing it to a desired power level to regulate accordingly the power level of an outgoing signal.